A magnetic resonance imaging apparatus is an apparatus which images the chemical and physical microscopic information of a substance or observes a chemical shift spectrum by using a phenomenon in which when a group of nuclei having a unique magnetic moment is placed in a uniform static field, they resonantly absorb the energy of a radio-frequency magnetic field that rotates at a specific frequency. Such a magnetic resonance imaging apparatus is very effective as a method of noninvasively obtaining an image of an anatomical slice of a human body. In particular, this apparatus is widely used as a diagnosis apparatus for a central nervous system such as the brain surrounded by the skull. On the other hand, the apparatus requires a long imaging time. It is therefore thought that there is room for improvement in diagnostic performance for a moving organ such as the heart.
Recently, a combination of an improvement in hardware around a gradient field system and high-speed scanning has increased the number of cases in which the magnetic resonance imaging apparatus can be used for cardiac examination. Myocardial perfusion imaging, in particular, is an imaging method which can image myocardial viability in the form of the progress of staining by a contrast medium by combining an ECG gate after the injection of the contrast medium and dynamic imaging. This method has attracted a great deal of attention as an examination method which can obtain effects that cannot be obtained by other diagnosis apparatuses.
When, however, cardiac examination is to be performed by using a magnetic resonance imaging apparatus, the following problems arise.
First of all, when the heart is to be imaged on a slice basis, it is possible to obtain an image with less influence of motion by high-speed imaging such as EPI (Echo Planar Imaging). When viewed in the phase direction of dynamic imaging, an image with motion artifacts is often obtained due to respiratory body motion, a cardiac phase shift, and the like.
One solution to prevent respiratory body motion artifacts is to make a patient (object) hold his/her breath. However, making a patient with a cardiac problem hold his/her breath will undesirably increase the examination load. In addition, heartbeats may change before and after breath holding.
Further, recently, a technique called non-contrast enhanced MRA has been developed in magnetic resonance imaging. This technique images blood vessels without using a contrast medium. However, if non-contrast enhanced MRA is performed by utilizing biological information (for example, respiratory period), the following problem may occur. That is, for example, when the respiratory period of a patient becomes extremely short, the imaging is carried out even in the state where the magnetization is not fully recovered.
Embodiments have been made in consideration of the above situation, and have as their object to provide a magnetic resonance imaging apparatus which can execute accurate myocardial perfusion imaging and non-contrast enhanced MRA without requiring breath holding by a patient by making a phase of dynamic imaging relatively correspond to a cardiac phase.